This lock is place below the whisper key and activated by the left thumb. Catalog Number: 31 Available On: Models 601, 660, 101, 201, I, II, III, & IV Conflicts With: While it does not actually conflict, it is not recommended at the same time as right hand whisper key locks. Required Deletion: Models 601, 660, 101, 201, I, II, III: Delete Right Hand Whisper Key Lock, Type II (39)